Mass-Change Acceleration in Antarctica from GRACE Monthly Gravity Field Solutions

2011 ◽  
pp. 591-596 ◽  
Author(s):  
Lóránt Földváry
Keyword(s):  
Gravity Field ◽  
Mass Change

scholarly journals Using Swarm to Detect Total Water Storage Changes in 26 Global Basins (Taking the Amazon Basin, Volga Basin and Zambezi Basin as Examples)

2021 ◽  
Vol 13 (14) ◽  
pp. 2659
Author(s):  
Zhengtao Wang ◽  
Kunjun Tian ◽  
Fupeng Li ◽  
Si Xiong ◽  
Yu Gao ◽  
...  
Keyword(s):  
Gravitational Field ◽  
Data Processing ◽  
Gravity Field ◽  
Water Storage ◽  
Mass Change ◽  
Time Varying ◽  
Processing Strategy ◽  
Terrestrial Water Storage ◽  
Total Water ◽  
Terrestrial Water

The Gravity Recovery and Climate Experiment (GRACE) satellite provides time-varying gravity field models that can detect total water storage change (TWSC) from April 2002 to June 2017, and its second-generation satellite, GRACE Follow-On (GRACE-FO), provides models from June 2018, so there is a one year gap. Swarm satellites are equipped with Global Positioning System (GPS) receivers, which can be used to recover the Earth’s time-varying gravitational field. Swarm’s time-varying gravitational field models (from December 2013 to June 2018) were solved by the International Combination Service for Time-variable Gravity Field Solutions (COST-G) and the Astronomical Institute of the Czech Academy of Sciences (ASI). On a timely scale, Swarm has the potential to fill the gap between the two generations of GRACE satellites. In this paper, using 26 global watersheds as the study area, first, we explored the optimal data processing strategy for Swarm and then obtained the Swarm-TWSC of each watershed based on the optimal results. Second, we evaluated Swarm’s accuracy in detecting regional water storage variations, analyzed the reasons for its superior and inferior performance in different regions, and systematically explored its potential in detecting terrestrial water storage changes in land areas. Finally, we constructed the time series of terrestrial water storage changes from 2002 to 2019 by combining GRACE, Swarm, and GRACE-FO for the Amazon, Volga, and Zambezi Basins. The results show that the optimal data processing strategy of Swarm is different from that of GRACE. The optimal results of Swarm-TWSC were explored in 26 watersheds worldwide; its accuracy is related to the area size, runoff volume, total annual mass change, and instantaneous mass change of the watershed itself, among which the latter is the main factor affecting Swarm-TWSC. Knowledge of the Swarm-TWSC of 26 basins constructed in this paper is important to study long-term water storage changes in basins.

Intercomparison of signals and noise in time variable gravity field releases from an ice sheet perspective

2020 ◽  
Author(s):  
Andreas Groh ◽  
Ulrich Meyer ◽  
Martin Lasser ◽  
Christoph Dahle ◽  
Andreas Kvas ◽  
...  
Keyword(s):  
Time Series ◽  
Gravity Field ◽  
Regional Integration ◽  
Noise Level ◽  
Ice Sheets ◽  
Product Evaluation ◽  
Time Variable ◽  
Mass Change ◽  
Time Variable Gravity ◽  
Variable Gravity

<p align="justify">The International Combination Service for Time-variable Gravity Fields (COST-G), a product center of IAG’s International Gravity Field Service, aims on the combination of monthly global gravity field models. A consolidated gravity field series is derived from individual releases provided by different analysis centres (AC). COST-G’s Product Evaluation Group (PEG) assesses the combined gravity field series as well as the series provided by the ACs regarding their suitability for studying mass changes in the Earth’s subsystems (e.g. oceans, cryosphere, continental hydrosphere). Here we present results from the PEG’s assessment regarding mass changes of the ice sheets. Our study focuses on the COST-G RL01 series and the contributing releases AIUB RL02, GFZ RL06, ITSG-Grace2018, CSR RL06 and an unconstrained variant of GRGS RL05.</p> <p align="justify">Based on residual variations of the spherical harmonic (SH) coefficients with respect to a long-term and seasonal model, we quantify the noise level of the latest GRACE/GRACE-FO solutions series provided by COST-G and the contributing ACs. This assessment is performed both in the SH domain and in the space domain, focusing on the polar regions. A regional integration approach using tailored sensitivity kernels is applied to derive mass change time series for individual drainage basins and the entire ice sheets in Greenland (GIS) and Antarctica (AIS). A measure for the noise level of the different mass change time series is inferred from the residuals with respect to a climatology, corrected for remaining inter-annual mass changes. In this way we are able to assess if and to which extent mass change products for GIS and AIS can benefit from the combination of different solution series. Furthermore, we also quantify the signal content inherent to the individual mass change time series in terms of the seasonal signal and the linear trend (i.e. mass balance). Differences in the signal content between the releases are further investigated with respect to contributions from different parts of the SH spectrum. In addition to selected SH coefficients (e.g. C<sub>21</sub>, S<sub>21</sub>), we systematically attribute the differences to each SH degree and the corresponding SH orders.</p>

Interannual Variability in Global Ocean Mass Derived from 18+ Years of GRACE and GRACE-FO Satellite Gravimetry

2021 ◽  
Author(s):  
Benjamin D. Gutknecht ◽  
Andreas Groh ◽  
Martin Horwath
Keyword(s):  
Gravity Field ◽  
Sea Level ◽  
Linear Trend ◽  
Mass Change ◽  
Global Ocean ◽  
Mass System ◽  
Quasi Biennial Oscillation ◽  
Data Set ◽  
Ocean Mass ◽  
Major Mode

<p>The combined 18+ years long time series of observations of the Earth's gravity field from the satellite missions GRACE and GRACE-FO provides us with an unprecedented opportunity to analyse mass change and re-distribution in the Earth system. Furthermore, as the mission continues, we may also gain more insight into those types of variability in the water mass system that act over time scales of several years and possibly even decades.</p><p>For our analysis presented here, we updated the previous Ocean Mass Change (OMC) product by the ESA CCI Sea Level Budget Closure project, including (1) corrections for Glacial Isostatic Adjustment, (2) restorement of GAD background fields, (3) subtraction of atmospheric mean fields, and (4) replacement of dedicated low-degree coefficients for centre-of-mass, oblateness (TN14) and C30 (TN14) in the spherical harmonic gravity field solutions. We applied least-squares minimisation of the residual of a multi-parameter functional fit to the OMC series, including i.a. linear trend, semi-/annual signals, and an optional quadratic fit. We analysed the complete residual series based on the four monthly GRACE and GRACE-FO RL06 solutions from CSR/GFZ/JPL and ITSG-Grace2018 after removal of linear trend and seasonal cycles.</p><p>The remaining signal shows clear evidence of interannual oscillations and correlates (>0.5) with the Multivariate ENSO index (MEI). By spectral analysis and by an independent simulated-annealing approach, we locate several primary modes of the residual between 130 and 29 months. The phase of the lowest of these partial frequencies approximates that of solar flux data representing the solar cycle and the shortest major mode resembles the frequency of the Quasi Biennial Oscillation. However, minor phase-shifts and a direct physical link in this regard are not yet fully understood. When we include the extra modes in our OMC minimisation approach, it can be shown that recent acceleration in global ocean mass may indeed be smaller than previously anticipated by quadratic fitting while neglecting longer wavelengths.</p><p>Furthermore, the extrapolation of the fit including three prominent interannual modes between 29 and 130 months is able to predict recent La Niña related negative ocean mass anomalies. Our findings might support and integrate in similar analyses of the global sea level and other ECVs elsewhere. However, we must emphasise that an analysis of near-decadal oscillations from a sub-20 year lasting data set is yet to become more stable with increasing observation length from GRACE-FO.</p>

Spherical and ellipsoidal surface mass change from GRACE time-variable gravity data

2020 ◽  
Author(s):  
Michal Šprlák ◽  
Khosro Ghobadi-Far ◽  
Shin-Chan Han ◽  
Pavel Novák
Keyword(s):  
Gravity Field ◽  
Gravitational Potential ◽  
Gravity Data ◽  
Time Variable ◽  
Mass Change ◽  
Spherical Approximation ◽  
Surface Mass ◽  
Time Variable Gravity ◽  
The Earth ◽  
Variable Gravity

<p>The problem of estimating mass redistribution from temporal variations of the Earth’s gravity field, such as those observed by GRACE, is non-unique. By approximating the Earth’s surface by a sphere, surface mass change can be uniquely determined from time-variable gravity data. Conventionally, the spherical approach of Wahr et al. (1998) is employed for computing the surface mass change caused, for example, by terrestrial water and glaciers. The accuracy of the GRACE Level 2 time-variable gravity data has improved due to updated background geophysical models or enhanced data processing. Moreover, time series analysis of ∼15 years of GRACE observations allows for determining inter-annual and seasonal changes with a significantly higher accuracy than individual monthly fields. Thus, the improved time-variable gravity data might not tolerate the spherical approximation introduced by Wahr et al. (1998).</p><p>A spheroid (an ellipsoid of revolution) represents a closer approximation of the Earth than a sphere, particularly in polar regions. Motivated by this fact, we develop a rigorous method for determining surface mass change on a spheroid. Our mathematical treatment is fully ellipsoidal as we concisely use Jacobi ellipsoidal coordinates and exploit the corresponding series expansions of the gravitational potential and of the surface mass. We provide a unique one-to-one relationship between the ellipsoidal spectrum of the surface mass and the ellipsoidal spectrum of the gravitational potential. This ellipsoidal spectral formula is more general and embeds the spherical approach by Wahr et al. (1998) as a special case. We also quantify the differences between the spherical and ellipsoidal approximations numerically by calculating the surface mass change rate in Antarctica and Greenland.</p><p> </p><p>References:</p><p>Wahr J, Molenaar M, Bryan F (1998) Time variability of the Earth’s gravity field: Hydrological and oceanic effects and their possible detection using GRACE. Journal of Geophysical Research: Solid Earth, 103(B12), 30205-30229.</p>

Glacial Contributions to 21st Century Sea Level Rise

Eos ◽  
2020 ◽  
Vol 101 ◽  
Author(s):  
Kate Wheeling
Keyword(s):  
Sea Level Rise ◽  
Sea Level ◽  
21St Century ◽  
Mass Change ◽  
Sources Of Uncertainty

Researchers identify the main sources of uncertainty in projections of global glacier mass change, which is expected to add about 8–16 centimeters to sea level, through this century.

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